THE EFFECTS OF PREEXISTING NORMAL FAULTS ON THRUST RAMP DEVELOPMENT -AN EXAMPLE FROM THE NORTHERN APENNINES, ITALY

The Umbria-Marche foreland fold-and-thrust belt in the northern Apenni nes of Italy provides excellent evidence to test the hypothesis of syn sedimentary-structural control on thrust ramp development. This orogen ic belt consists of platform and pelagic carbonates, Late Triassic to Miocene in age, whose deposition was controlled by significant synsedi mentary extension. Normal faulting, mainly active from Jurassic throug h Late Cretaceous-Paleogene time, resulted in significant lateral thic kness variability within the related stratigraphic sequences. By Late Miocene time the sedimentary cover was detached from the underlying ba sement and was deformed by east-verging folds and west-dipping thrusts . Two restored balanced cross sections through the southernmost part o f the belt show a coincidence between the early synsedimentary normal faults and the late thrust fault ramps. These evidences suggest that s ynsedimentary tectonic structures, such as faults and the related lith ological lateral changes, can be regarded as mechanically important co ntrolling factors in the process of thrust ramp development during pos itive tectonic inversion processes.